I'm getting an "invalid credit card" on a form using this plugin with a card that was just tested elsewhere without trouble. No other error messages are available, but I did just upgrade GF to 1.7.2 and wondering if that has something to do with it.

don't know if this will help, but i started getting array messages again after putting in a Captcha field. I installed Really Simple Captcha and used the math challenge, after which the array errors disappeared.